Study tracks turtles in marine 'desert'

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PALO ALTO, Calif., Feb. 9 (UPI) -- Tracking leatherback sea turtles has produced insights into why they hang out in part of the South Pacific long considered a marine wasteland, researchers say.

Scientists at Stanford University tagged turtles for a five-year study that has revealed why the shelled reptiles congregate for months in what appeared to be one of the most nutrient-poor regions in the oceans, known as the South Pacific Gyre, a Stanford release reported Tuesday.

Until now, researchers didn't know why leatherbacks head for the gyre and linger for months. Satellite data suggested this area of the Pacific Ocean between South America and New Zealand appeared to be a virtual desert in the ocean, largely devoid of nutrients.

However, researchers say, the presence of substantial tuna and swordfish fisheries in region suggested there might be ample food of some sort available.

Because only limited data existed about the distribution of the leatherback's favorite prey, jellyfish, in the gyre, no one knew whether the turtles were finding food there or not.

"Nobody is really out chasing jellyfish down," Stanford biologist George Shillinger said. "They are poorly studied organisms and there is very little data on them in the region of the gyre."

But data from the tagged turtles suggested there may be plenty of jellyfish for the turtles to pursue.

"We saw a distinct reduction in the swimming speed of the turtles as they entered the South Pacific Gyre," Shillinger said. "They were making more turns, diving more frequently and diving deeper. All those things suggest feeding behavior."

The turtles are often at risk from commercial fishing operations as the make their way from Costa Rican breeding grounds to open waters, researchers say.

"Understanding what sort of areas leatherbacks are likely to favor is a critical first step in protecting them in the open ocean," Shillinger said.